There are two kinds of film-forming methods for Organic Light Emitting Diode (OLED): evaporation process and solution-based process. The evaporation process is relatively mature for small size OLED, and has been applied to mass production currently. The solution-based process mainly comprise inkjet printing, nozzle coating, spin coating and screen printing, etc. The inkjet printing technique is considered as an important method for large size OLED to achieve mass production, due to high efficiency of material utilization and implementation of large size.
In the inkjet printing process, a pixel define layer (Bank) needs to be manufactured on electrodes of a substrate in advance to define that the ink flows into a specified sub-pixel region accurately. An upper surface of the pixel define layer requires a hydrophobic material with low surface energy to ensure that the ink would not ooze to the outside of the pixel to result in color mixture between the pixels. An inclined surface of the pixel define layer requires a hydrophilic material with high surface energy to ensure that the liquids can spread on a conductive glass within the pixel without an aperture. In addition, luminous efficiency of a light emitting display is also a bottleneck for materials.
As to the existing pixel define layer with trapezoid shape, after the hydrophobic treatment, the organic layer spreads badly. There may exist an un-spreading region at the edges of the conductive glass and the pixel define layer, which may, after evaporation of cathodes, cause cathode and anode short circuit to leakage. The pixel define layer with reversed trapezoid shape may allow the ink to spread well within the pixel. However such the pixel define layer may reduce discontinuous light emitting region of the cathode. Therefore it needs to increase film thickness or evaporate the cathode thickly. A double-layer pixel define layer with trapezoid shape may avoid the cathode and anode short circuit in a single-layer pixel define layer, and may be possible to reduce the light emitting region.